This invention relates to evaporative cooling systems and more particularly to cool towers.
Natural draft evaporative coolers, popularly known as "cool towers", are recent developments which provide very low cost cooling in dry climates. These towers are used for cooling residences, wind sheltered outdoor areas, and even bus stops, and are found in the southwestern United States and Saudi Arabia.
Operation of the towers depends on the density difference between the tower and outside air. Evaporative cooling pads located around the upper tower perimeter fill the tower with cool air at a higher density than ambient air. The cooler air falls through the tower at a rate which depends on the magnitude of the density difference, the height of the tower, the resistance to air flow provided by the tower and the associated structure, and wind forces on the tower-structure envelope.
As the humidity of the outside air increases, performance of the tower decreases. Because of this, the range of cool towers is extremely limited, usually to areas having particularly dry environs.
In traditional evaporative coolers, a group of developments have arisen which attempt to widen the range of evaporative coolers into more humid environs. These include two-stage cooling systems.
A number of two stage evaporative cooling systems have been developed and are described in depth by Evaporative Air Conditioning Handbook, 2nd Ed, Chapmann & Hall, New York, incorporated herein by reference.
All require a first stage heat exchanger which cools outside air without humidification. The pre-cooled air, with a reduced wet bulb temperature, is further cooled by evaporation of water in the second stage evaporative cooler. Heat is also rejected from the first stage heat exchanger by evaporation, either in an external cooling tower or using an additional evaporative cooler, depending on the type of heat exchanger used.
In U.S. Pat. No. 4,532,777, entitled "Two Stage Cooling System" issued to Thompson on Aug. 6, 1985, a two stage cooler is described which utilizes two evaporative steps wherein an oil-like material is cooled by contact with evaporating water. The cooled oil-like material is used to pre-cool, without humidifying, air before a second evaporative cooling step. This patent is incorporated hereinto by reference.
Unfortunately, in many applications, a ready source of electricity does not exist to power the re-circulating pumps, the blowers and other equipment necessary for two stage coolers to operate.
It is clear from the foregoing that an energy efficient cooling mechanism does not exist that can operate in humid environments.